The present inventions pertain to the field of documents, including more particularly to novel duplication resistant documents.
The importance of making documents safe from duplication and alteration is readily apparent. The advent of improved photocopy equipment, particularly high resolution digital color photocopy equipment, as well as desk top publishing and digital scanning, has provided the unscrupulous with the means for unauthorized duplication of original documents for the purpose of passing them off, with or without alteration, as the original document. The quality of the reproductions obtainable through these means is so good that it is difficult to distinguish original copies from color reproductions. Even if the duplication is not exact, the reproduction often appears authentic in the absence of the original for comparison. This problem is well-known to the issuers of such original documentation, and considerable attention has been given to find ways and means to prevent unauthorized duplication of such documents by photocopiers or other electronic methods.
Many techniques have been developed to prevent improper reproduction of original documents. One of the more known techniques is based on the phenomenon that photographic copiers have an element value (sometimes referred to as element frequency) threshold above which the photocopier is unable to distinguish the individual elements of the pattern of halftone printing. In general, a pattern with a low line screen value of large sized elements is more easily reproducible than a pattern with a high line screen value of small sized elements.
In accordance with this technique, a hidden warning message, such as xe2x80x9cVOIDxe2x80x9d or xe2x80x9cCOPY,xe2x80x9d is printed in a halftone over a halftone background printed on a substrate. The line screen value of the hidden warning message is selected, such that the halftone elements of the hidden warning message are reproduced when photocopied. The line screen value of the background, however, is selected, such that the halftone elements of the background are not reproduced when photocopied. As a result, the hidden warning message will appear on duplicates of the original document made by photocopying. This method is also used by reversing the halftones of the hidden warning message and the background, such that the elements of the hidden warning message are not reproduced and the elements of the background are reproduced when photocopied or scanned.
In addition to selecting differing line screen values for the hidden warning message and the background pattern to allow them to be used to prevent duplication, it is also known to select differing tonal screen values (i.e., the percentage of ink coverage), so that the hidden warning message more easily appears on a reproduction of the original document.
Because of the disparity between the respective line screen values and respective tonal screen values of the hidden warning message and background pattern, a mere combination of these two techniques would not be effective, because the hidden warning message would normally be visible to a casual observer of the original. To minimize the visible appearance of the warning message with this combined technique, the respective tonal screen values are selected so that they are more similar, and/or a camouflage pattern can be printed over, or combined with, the hidden warning message and background to help obscure the hidden warning message from a casual observer of the original document. A description of these aforementioned techniques can be found in U.S. Pat. Nos. 4,227,720 and 5,197,795.
While the above techniques have provided some degree of protection of original documents with respect to most copiers, in recent years digital scanners and color copiers have improved substantially. These new color copiers, such as the Canon 800 and 1000 series, have made the above techniques less effective in protecting original documents. By manipulating the control settings on such devices, copies can be made of such original documents in which the hidden warning message does not readily appear on reproductions when some of the most commonly used frequency and element size combinations are used. When the contrast setting of these modern photocopiers is set to the lighter settings or the copier is set to a built-in halftone setting, the resolution of the copier is such that it reproduces neither the lower line screen value/high tonal screen value hidden warning message nor the higher line screen value/lower tonal screen value background pattern. If the line screen value and tonal screen value of the hidden warning message is adjusted so that the lower line screen value/high tonal screen value hidden warning message is reproduced at a lighter copier setting, both the higher line screen value/lower tonal screen value background pattern and the lower line screen value/higher tonal screen value hidden warning message are reproduced. In both cases, the hidden warning message does not readily appear on the reproduction of the original document, so that a casual observer of the document may not be alerted that the document in possession is not the original.
A greater disparity between the respective line screen values and tonal screen values of the hidden warning message and background pattern would allow the hidden warning message to appear on a reproduction of the original document even with the manipulation of the copier. Due to the great disparity, however, most presently known camouflage techniques do not adequately suppress the visual appearance of the hidden warning message on the original document. This could result in the original document being rejected as a copy, which would not be acceptable to issuers of the original.
Recently, a camouflaging technique has become available, whereby a dynamic camouflaging layer composed of an environmentally density changing ink, such as thermochromic ink, is used to camouflage a hidden warning message formed by a contrasting layer similar to those described above. In accordance with this technique, the density of the dynamic camouflaging layer, which is normally great enough to camouflage the hidden warning message, decreases when the original document is copied, thereby exhibiting the latent warning message on the copy. Thus, the dynamic nature of the camouflaging layer allows the disparity of the contrasting layer that makes up the hidden warning message to exhibit a greater disparity than otherwise allowed by a non-dynamic camouflaging layer. Details concerning the use of such dynamic camouflaging techniques are described in copending application Ser. No. 09/046,571, which is fully and expressly incorporated herein by reference.
Although the aforementioned dynamic camouflaging technique is generally successful in precluding an unscrupulous copyist from suppressing the hidden warning message on a reproduction of the original document, future developments in copier technology necessitate continued improvements in techniques used to prevent counterfeiting of original documents. These improved techniques can be either independent from, or combined with, dynamic camouflaging or other techniques.
The present invention comprises a document and method of producing, such a document that, when reproduced, exhibits a latent message.
In accordance with a first aspect of the present inventions, a document comprises a substrate and a nano-pattern disposed on the substrate, wherein the nano-pattern is configured for forming a latent message (e.g., a warning or alert message) that appears on a copy of the document. For example, the nano-pattern can form either the foreground or the background of the latent message, and be configured, such that the foreground or background exhibits a first visual density on the original document, and a second visual density greater than the first visual density on the copied document.
In the preferred embodiment, the nano-pattern forms one of a foreground and a background of the latent message; and another pattern, e.g., a conventional halftone or screened pattern or another nano-pattern, forms the other of the foreground and background of the latent message. The nano-pattern and the other pattern are configured, such that the foreground and background exhibit substantially similar visual densities on an original of the document, and exhibit substantially different visual densities on the copied document. This can be accomplished by forming the nano-pattern with a plurality of adjacent elements that are configured to trap printing matter, such as ink or toner, when electronically copied, thereby darkening the nano-pattern on the copied document. Trapping of the printing matter is facilitated by the design and miniature size of the adjacent elements, which are preferably less than two-point print, and most preferably, less than one and one-half point print or less. The plurality of adjacent elements that make up the nano-pattern can be combined into a series of nano-structures, e.g., polygons, circles or ovals, crosses or x""s, or alpha-numerical characters, to produce the desired darkening effect. The series of nano-structures can either be uniformly sized and spaced, resulting in a regular nano-pattern, or variably sized and spaced, resulting in an irregular nano-pattern. Additionally, the variably sized and spaced nano-structures can be configured in a modulation pattern to form the variably sized and spaced nano-pattern.
In accordance with a second aspect of the present inventions, a document comprises a substrate and a latent message formed by a pattern that is configured for trapping printing matter, e.g., ink or toner, when electronically copied. For example, the pattern can be formed of a plurality of adjacent rectilinear elements and/or curvilinear elements that coordinate with each other to trap the printing matter. In this manner, the latent message is darkened, and thus activated, on a copy of the document.
In the preferred embodiment, the pattern forms one of a foreground and a background of the latent message, and another pattern forms the other of the foreground and background of the latent message. The two patterns are configured to respectively exhibit first and second visual densities on the original document, and respectively exhibit s third and fourth visual densities on the copied document, wherein the first and second visual densities are substantially similar, and the third and fourth visual densities are substantially different.
In accordance with a third aspect of the present inventions, a document comprises a substrate and a nano-pattern disposed on the substrate, wherein the nano-pattern is configured for forming a latent message (e.g., a warning or alert message) that appears on a copy of the document. The document further comprises a camouflage pattern disposed on the substrate, wherein the camouflage pattern coincides with the latent message. The camouflage pattern can be composed of a standard ink or environmentally changing ink, such as a thermochromic ink.
If a thermochromic ink is used for the camouflage pattern, it preferably exhibits a visual density that is inversely proportional to the ambient temperature. For example, the thermochromic ink can have a cold density, such that the camouflage pattern is inactivated at room temperatures, and a warm density, such that the camouflage pattern is activated at scanning temperatures. In this manner, when inactivated, the camouflage pattern suppresses the latent message on the original document, and when activated, exhibits the latent message on the copied document.